This invention relates to an integrated process for the preparation of substantially linear high molecular weight thermoplastic polymers derived from aryl polyhalide monomers. More particularly, the invention relates to the intermediate preparation of aryl polyhalide monomers in a liquid phase of an aprotic solvent and an azeotrope former wherein water is removed from the reaction mass as an azeotrope until substantially anhydrous conditions are attained. The aryl polyhalide monomers are then coupled through carbon-to-carbon bonding by contacting the monomers with a catalyst mixture of a nickel compound and a ligand in the presence of a reducing metal and an aprotic solvent under substantially anhydrous conditions to form a substantially linear high molecular weight themoplastic polymer.
Polymerization reactions which form carbon-to-carbon bonds are few although they are extremely useful in organic synthesis. Copending U.S. patent application Ser. No. 072,309, filed Sept. 11, 1979, describes the coupling of aryl and heteroaryl polyhalide monomers in an aprotic solvent under anhydrous conditions using a catalyst mixture of a nickel compound and a ligand in the presence of a reducing metal. This copending application describes the only presently known aryl-aryl coupling process which is capable of producing high molecular weight polymers. The present invention enhances the practicality of copending U.S. patent application Ser. No. 072,309 in terms of material handling and economics. The substantially linear high molecular weight thermoplastic polymers prepared in accordance with the integrated process of the present invention are relatively inexpensive and also relatively simple to prepare. These polymers exhibit excellent strength and toughness properties as well as outstanding thermal, oxidative and chemical stability. They find wide utility in the production of shaped and molded articles where such properties are necessary and are highly desirable and also in the preparation of film and fiber products which have excellent mechanical properties.
Heretofore, both the isolation and purification of aryl polyhalide monomers have been required before contacting the monomers with a catalyst mixture of a metal compound to form thermoplastic polymers as described in copending U.S. patent application Ser. No. 072,309. It has been demonstrated that in the instant polymerization reaction the solvent must be maintained substantially anhydrous before and during the reaction. While amounts of water up to about 0.01 percent can be tolerated, amounts of water substantially greater than this are desirably avoided as the reaction of water with the aryl polyhalide monomers in the presence of an active catalyst leads to reduction and only low molecular weight products are secured. It has been demonstrated in copending U.S. patent application Ser. No. 302,691, filed Sept. 15, 1981, now abandoned, that aryl halides can be efficiently reduced by water in the presence of a nickel catalyst as utilized in the instant invention. The reaction of water with the catalyst mixture also leads to the deactivation of the active catalyst. In order to secure the production of substantially linear high molecular weight thermoplastic polymers, the reaction system should be substantially anhydrous and preferably with less than 0.01 percent by weight water in the polymerization reaction mixture. Thus, it is desirable to provide an integrated process directed to the intermediate preparation of aryl polyhalide monomers with the simultaneous removal of substantially all water therefrom, thereby eliminating the need for further procedural steps, such as isolation and purification of the aryl polyhalide monomers and the resulting problems of handling and expense attributable to these steps, before the aryl polyhalide monomers can be directly contacted with a catalyst mixture in the presence of a reducing metal and an aprotic solvent under anhydrous conditions to form substantially linear high molecular weight thermoplastic polymers.
It is completely unexpected that an integrated process can be employed for the preparation of substantially linear high molecular weight thermoplastic polymers due to the known ease of reduction of aryl halides caused by trace amounts of water and the sensitivity, e.g., deactivation, of the catalyst mixture to water. According to the present invention, it has now been discovered that the addition of an azeotrope former, e.g., toluene, to an aprotic solvent effectively removes water from an aryl polyhalide monomer reaction mixture until sufficient anhydrous conditions are attained for directly contacting the aryl polyhalide monomers with a catalyst mixture in the presence of a reducing metal and an aprotic solvent under substantially anhydrous conditions to form substantially linear high molecular weight thermoplastic polymers by carbon-to-carbon bond polymerization. As a result of the present invention, there is no longer a need for isolation and purification of an aryl polyhalide monomer mixture before effectively employing the mixture in a carbon-to-carbon bond polymerization reaction. The additional problems of handling and expense attributable to the isolation and purification steps are also eliminated by the integrated process of this invention. Sufficient anhydrous conditions are attained in the integrated process of the instant invention so as to effectively prevent the reduction of the aryl polyhalide monomers, prevent the deactivation of the water-sensitive catalyst mixture and thus provide for the efficient preparation of substantially linear high molecular weight thermoplastic polymers.
U.S. Pat. No. 4,263,466 describes a method of coupling aryl and heteroaryl mono chlorides in an aprotic solvent under an inert atmosphere by employing a catalyst mixture of nickel compound and a ligand in the presence of a reducing metal to form coupled products, e.g., biphenyl compounds.
U.S. Pat. No. 4,175,175 and U.S. Pat. No. 4,108,837 describe high molecular weight polyarylene polyethers which are the linear thermoplastic reaction products of an alkali metal double salt of a dihydric phenol, e.g., dipotassium salt of 2,2-bis(4-hydroxyphenyl)propane, and a dihalobenzenoid compound, e.g., 4,4'-dichlorophenylsulfone. The polymers have a basic structure composed of recurring units having the formula EQU --O--E--O--E'--
wherein E is the residuum of the dihydric phenol and E' is the residuum of the dihalobenzenoid compound, both of which are valently bonded to the ether oxygen through aromatic carbon atoms. The polymerization reaction is conducted in a liquid phase of a sulfoxide or sulfone organic solvent and an azeotrope former such as chlorobenzene, dichlorobenzene and xylene. Water is removed from the reaction as an azeotrope with the azeotrope former to avoid the reaction of water with the dihalobenzenoid compound which leads to the formation of phenolic species and only low molecular weight products are secured. It is stated that water amounts of 0.5 weight percent may be tolerated in the process of these two patents. This is in contrast to the instant invention in which it is critical that azeotropic removal provide sufficient dryness, i.e., 0.01 weight percent, to allow the formation of high molecular weight polymers.
Michio Zembayashi, Kohei Tamao, Jun-ichi Yoshida and Makoto Kumada, Nickel-Phosphine Complex-Catalyzed Homo Coupling of Aryl Halides in the Presence of Zinc Powder, Tetrahedron Letters No. 47, 4089-4092 (1977), printed in Great Britain, discloses the nickel-phosphine complex-catalyzed homo coupling of aryl halides in the presence of zinc powder. Specifically, Table I on page 4090 summarizes the results of homo coupling of bromobenzene to biphenyl under various conditions. Dimethylformamide is stated to be the most suitable solvent in the coupling reaction. The reaction is carried out in the presence of [Ni(PPh.sub.3).sub.2 Cl.sub.2 ], triphenylphosphine and zinc powder at a temperature of 50.degree. C. as described on page 4090. Table II on page 4091 describes the homo coupling of various organic bromide compounds to biphenyl. The reference additionally states on page 4091 that the addition of iodide ions to the reaction mixture greatly accelerates the coupling reaction.
Takakazu Yamamoto, Yasuhiro Hayashi and Akio Yamamoto, A Novel Type of Polycondensation Utilizing Transition Metal-Catalyzed C-C Coupling. I. Preparation of Thermostable Polyphenylene Type Polymers, Bulletin of the Chemical Society of Japan, Vol. 51 (7), 2091-2097 (1978) and Japanese Kokai Sho No. 52-154900/77 describes the polycondensation of di- and polyhalogenated organic compounds via magnesium Grignard reagents in the presence of of a transition metal catalyst to produce polyphenylene type polymers. The catalysts include di- and trivalent compounds such as NiCl.sub.2 (2,2'-bipyridine), NiBr.sub.2 (triphenylphosphine), PdCl.sub.2 (2,2'-bipyridine), NiCl.sub.2, CaCl.sub.2, FeCl.sub.2 and FeCl.sub.3. The reaction is conducted in ether solvents such as tetrahydrofuran, dibutyl ether and diglyme. The work of Yamamoto et al. is a stated extension of well known prior art on the coupling of aromatic Grignard reagents with aryl halides.
However, none of these references disclose an integrated process for the preparation of substantially linear high molecular weight thermoplastic polymers derived from the carbon-to-carbon bond polymerization of aryl polyhalide monomers under substantially anhydrous conditions as disclosed in the instant invention.